1. Field of the Invention
The present invention generally relates to a control apparatus for an AC generator of a motor vehicle and more particularly to a control apparatus for an AC generator of a motor vehicle for changing over power supply to a high-voltage electric load driven at a higher voltage level than an ordinary one.
2. Description of Related Art
For having better understanding of the present invention, background techniques thereof will be described in some detail. FIG. 6 is a circuit diagram showing a structure of a conventional control apparatus for an AC generator of a motor vehicle known heretofore such as disclosed, for example, in Japanese Unexamined Patent Application Publication No. 206848/1989 (JP-A-1-206848). Referring to the figure, the conventional control apparatus is comprised of an AC generator (alternating current generator) 1 driven by an internal combustion engine of a motor vehicle (not shown) and constituted by a field coil 102 for generating a rotating magnetic field and an armature coil 101 for generating an AC voltage under the action of the rotating magnetic field as generated, a rectifier 2 for full-wave rectification of the electric power generated by the AC generator 1, an output change-over controller 7 for changing over the supply of the rectified output power of the rectifier 2 between a battery 4 and a high-voltage onboard electric load (e.g. high-voltage equipment of a motor vehicle) 5, a key switch 6 which is closed for starting operation of the internal combustion engine by connecting a pulse terminal (i.e., terminal of positive polarity) of the battery 4 to the field coil 102 via the output change-over controller 7 for allowing a field current to flow through the field coil 102, an engine control unit 8 (hereinafter referred to as the ECU for short) for outputting an ON/OFF signal to an excitation switch 72 for allowing supply of the output of the ECU 8 for a predetermined time, and a voltage regulator 3 for regulating the generated voltage by controlling the exciting current of the field coil 102 in dependence on the terminal voltage of the battery 4.
The voltage regulator 3 is implemented in a circuit configuration described below. Connected between the plus terminal of the battery 4 and a grounded minus terminal 202 of the rectifier 2 are voltage division resistors 301 and 302 which serve as a first voltage detection means, wherein the terminal voltage of the battery 4 is detected as a divided voltage which makes appearance at a voltage dividing point A between the voltage division resistors 301 and 302. Further, voltage division resistors 313, 308 and 309 are connected in series between the plus terminal 201 and the minus terminal 202 of the rectifier 2 to serve as a second detection means and a third detecting means, respectively. The rectified output voltage making appearance at the plus terminal 201 is detected as a divided voltage appearing at a voltage dividing point B between a third detection means constituted by voltage division resistors 313 and 308 and the resistor 309.
Connected between the excitation terminal of the positive polarity and a minus terminal 202 is a transistor 304 which has a collector connected to a load resistor 306 and an emitter connected to the ground potential, wherein the base of the transistor 304 is connected to the anode of a Zener diode 303 which has a cathode to which cathodes of diodes 310 and 311 having anodes connected to the voltage dividing points A and B, respectively, are connected in common. These diodes 310 and 311 serve for isolating the first detection means and the second detection means, respectively. Furthermore, a diode 312 is connected between the voltage dividing point C and the plus excitation terminal (i.e., terminal of positive polarity) of the field coil 102. The diode 312 isolates the second detection means and the third detection means from each other.
Thus, it is apparent that each of the diodes 310, 311 and 312 is constituted by a reverse blocking diode provided for isolating the detection means from each other. The Zener diode 303 is turned on (i.e., becomes conducting) when the voltages appearing at the circuit points A and B reach a predetermined level to thereby allow the transistor 304 to become conducting (or assume on-state).
Further, connected between the plus excitation terminal and the minus terminal 202 is an output transistor 305 having a collector connected to a diode 307 and an emitter connected to the ground potential, wherein the bases of the output transistor 305 is connected to the collector of the transistor 304.
Parenthetically, the collector of the output transistor 305 is connected to the minus excitation terminal of the field coil 102. Thus, the diode 307 is connected in parallel to the field coil 102 and serves for absorbing a surge of relatively long duration generated in the field coil 102 upon turning off the output transistor 305.
Now, description will turn to operation of the AC generator control apparatus of the structure described above. Ordinarily, the output change-over switch 71 of the output change-over controller 7 is changed over toward the battery 4, whereby the ordinary operation mode (battery charging operation mode) is set. On the other hand, when the output change-over switch 71 is changed over to the high-voltage onboard electric load 5 for a short time (e.g. about five minutes), a high-voltage operation mode is validated, which mode is validated for activating, for example, a defrosting/defreezing system for removing ice adhering or sticking to window glass of motor vehicles in winter or in severe cold districts. This operation mode is changed-over from the ordinary operation mode. The high-voltage onboard electric load 5 may be constituted by a heater, for example.
In the first place, the ordinary operation mode will be elucidated. When the key switch 6 is closed for starting operation of the internal combustion engine to thereby close the excitation switch 72, field current flows to the field coil 102 from the battery 4 via the key switch 6 and the excitation switch 72. Thus, the AC generator 1 is set to the state ready for generation of an AC power. Subsequently, when the AC generator 1 starts electric power generation upon starting of the engine operation, the voltage appearing at the plus terminal 201 of the rectifier 2 rises up. The battery 4 is charged with the rectifier output via the output change-over switch 71, resulting in that the terminal voltage of the battery 4 rises up.
The terminal voltage of the battery 4 is detected in terms of a divided voltage resulting from the voltage division by the voltage division resistors 301 and 302 incorporated in the voltage regulator 3. When the divided voltage making appearance at the voltage dividing point A between the voltage division resistors 301 and 302 reaches a turn-on voltage of the Zener diode 303 as the terminal voltage of the battery 4 increases, the Zener diode 303 becomes conducting, whereby the transistor 304 is turned on while the output transistor 305 is turned off to thereby interrupt the field current. By contrast, when the terminal voltage of the battery 4 lowers below the predetermined level mentioned previously, the Zener diode 303 is set to the non-conducting or off-state. As a result of this, the output transistor 305 is tuned on to allow the field current to flow.
In this manner, the transistor 304 is repetitionally turned on and off as the Zener diode 303 assumes the on- and off-states respectively, as a result of which the output transistor 305 is repeatedly turned on and off to effect an intermittent interruption control of the field current flowing through the field coil 102 for thereby regulating the terminal voltage of the battery 4. In case a wire interconnecting the battery voltage detection terminal and the first detection means for detecting the terminal voltage of the battery 4 should be broken due to vibration of the internal combustion engine or for any other reason, the terminal voltage detecting operation will be rendered impossible because the battery terminal voltage can no more be applied to the first detection means which is constituted by the voltage division resistors 301 and 302.
In that case, however, the battery terminal voltage is supplied to the plus excitation terminal of the field coil 102 from the battery 4 via the key switch 6 and the excitation switch 72. Thus, the battery terminal voltage is applied to the second detection means (constituted by the voltage division resistors 308 and 309) via the diode 312. Consequently, the battery terminal voltage can be detected by the second detection means in terms of a divided voltage making appearance at the voltage dividing point B between the voltage division resistors 308 and 309.
In the second detection means, the voltage division resistance ratio is so dimensioned as to be slightly greater than that of the first detection means for obtaining the divided voltage for making the Zener diode 303 conducting. Accordingly, the charging voltage can be controlled even when the battery terminal voltage is not fed back due to the wire breakage, whereby the battery 4 can be prevented from being overcharged. Thus, the battery 4 can be protected against damage due to the overcharge.
Now, description will turn to a high-voltage operation mode in which the generator output is changed over to the high-voltage onboard electric load 5. For changing over the output of the rectifier 2, the excitation switch 72 is previously opened once under the control of the engine control unit 8 for damping the field current with a view to protecting the switch contacts from injury due to spark possibly produced in the output change-over switch 71.
After lapse of a predetermined time required for the attenuation of the field current, the output change-over switch 71 is changed over to the high-voltage onboard electric load 5, whereon the excitation switch 72 is closed under the control of the engine control unit 8. The sequential control of the change-over switch such as mentioned above can be appropriately programmed in a processing unit incorporated in the output change-over controller 7 in a conventional manner which will readily occur to those skilled in the art without any further elucidation. When the field current flows through the field coil 102 upon closing of the excitation switch 72, the voltage generated by the AC generator 1 increases, incurring a corresponding rise-up of the rectifier output voltage making appearance at the plus terminal 201.
In the high-voltage operation mode, the output of the rectifier 2 is disconnected from the battery 4. Consequently, the first and second detection means are rendered inactive. Thus, the terminal voltage of the plus terminal 201 is detected by the third detection means constituted by the voltage division resistors 313, 308 and 309. In this conjunction, it is to be noted that when the detection voltage for making the Zener diode 303 conducting is to be derived through the third detection means, the voltage division resistance ratio is so dimensioned that the voltage applied to the third detection means is higher than that applied to the first detection means.
More specifically, when the output of the rectifier 2 exceeds a preset high-voltage level determined by the resistance values of the voltage division resistors 313, 308 and 309 and the 303, the latter becomes conducting to thereby turn on the transistor 304 while the output transistor 305 being turned off. Subsequently, the rectified output voltage of the rectifier 2 is regulated to the preset high-voltage level by interrupting the field current to thereby stop the electric power generating operation. In this manner, the rectifier output of a proper value can be supplied directly to the high-voltage onboard electric load 5 such as a heater of a defreezing/defrosting system.
During the high-voltage supply operation described above, the battery 4 is not charged but assumes the discharging state for supplying only the field current to the AC generator 1. For this reason, the high voltage supplying operation is limited to a short duration (e.g. about five minutes) in order to prevent the excessive discharge or overdischarge of the battery 4. On the other hand, when the terminal voltage of the battery 4 lowers below a preset level, the high-voltage load operation is stopped for thereby allowing the ordinary battery charging operation mode to be resorted. It will readily be understood without need for any further description that the sequential control described above can be carried out by executing a corresponding program with the processing unit incorporated in the output change-over circuit 7. Incidentally, FIG. 7 is a waveform diagram for illustrating operations in the state where the output of the AC generator 1 is changed over to the high-voltage onboard electric load 5.
The conventional AC generator control apparatus described above has a drawback that upon changing over of the operation mode from the ordinary battery charging operation to the high-voltage onboard-load power supply operation, the output of the AC generator rises up steeply, incurring problems such as belt slippage, lowering of engine rotation speed (rpm) due to steep increasing of engine load and the like. For coping with those problems, there has been proposed a method for controlling the output of the AC generator so that it increases gradually or progressively by putting into operation the onboard electric load in the battery charging operation mode and subsequently performing the change-over operation mentioned previously.
At this juncture, however, it is required that the time taken for controlling progressively or gradually (referred to as the gradual control time) the output power of the AC generator be constant independent of difference in the power demand upon changing-over of the loads. In this conjunction, the gradual control time set on the presumption that the operation mode from the AC generator high-power output operation mode (high-voltage operation) is changed over to the AC generator low-power output operation mode (battery charging operation mode) is relatively short. Consequently, upon operation mode changing-over or transition from the low-output operation mode (battery charging operation mode) to the AC generator high output mode (high-voltage operation mode), there arise problems such as belts slippage, lowering of engine rotation speed (rpm) and the like due to steep increase of the output power of the AC generator.
On the other hand, when the progressive control time is determined on the presumption that the AC generator output power is to be changed over from the low output power (battery charging operation mode) to the high AC generator output power (high-voltage operation mode), the aforementioned progressive control time is relatively long. Consequently, upon transition from the high AC generator output (high-voltage operation mode) to the low output (battery charging operation mode), the output power of the AC generator will unnecessarily be suppressed in excess, incurring possibly a problem that power demand required by loads such as illuminating lamps of the motor vehicle can not be accommodated due to overdischarge of the battery.
In the light of the state of the art described above, it is an object of the present invention to provide a control apparatus for an AC generator of a motor vehicle, which apparatus is substantially immune to the problems of the conventional control apparatuses described above.
More particularly, it is an object of the present invention to provide a control apparatus for an AC generator of a motor vehicle which can solve or mitigate the problem of variation of the engine rotation speed due to steep increase of the AC generator output power and/or steep decrease or increase of engine load as brought about by the change-over of the operation modes mentioned above regardless of difference in the output power of the AC generator between the different operation modes.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention a control apparatus for an AC generator of a motor vehicle, which apparatus includes a rectifier for rectifying a voltage generated by an AC generator which is driven by an internal combustion engine and includes a field coil, a battery charged with electric energy outputted from the rectifier, a high-voltage electric load of the motor vehicle supplied with electric energy from the output of the rectifier, a mode setting means for changing over the output of the rectifier to the battery or the high-voltage electric load of the motor vehicle to thereby set a battery charging operation mode or a high-voltage operation mode, and a voltage regulator for controlling a field current flowing through the field coil so that the field current increases gradually at rate of changes set for the operation modes, respectively, to thereby regulate an output voltage of the AC generator to a predetermined value in each of the operation modes as set.
In a preferred mode for carrying out the invention, the mode setting means may be adapted to set the battery charging operation mode or the high-voltage operation mode and output a control signal indicative of the rate of change of the field current in each of the operation modes. The voltage regulator changes over the operation modes of the AC generator by controlling the field current in accordance with the control signal.
In another preferred mode for carrying out the invention, the voltage regulator may include an identifying means for identifying discriminatively content of the control signal outputted from the mode setting means, a rate-of-change setting means for setting the rate of change of the field current on the basis of result of the identification of the control signal, and a current control means for controlling gradual increase of the field current in accordance with the rate of change as set.
In yet another preferred mode for carrying out the invention, the mode setting means may output a control signal for setting a low-voltage operation mode upon changing over to the high-voltage operation mode from the battery charging operation mode or upon changing over to the battery charging operation mode from the high-voltage operation mode. The current control means may then respond to the control signal for setting the low-voltage operation mode to thereby decrease the field current lower than the field current in the battery charging operation mode and the high-voltage operation mode.
In still another preferred mode for carrying out the invention, the mode setting means may be so arranged as to output the control signals for the operation modes, respectively, in the form of pulse train signals which differ from each other in respect to duty ratio.
In a further preferred mode for carrying out the invention, the mode setting means may be so arranged as to output the control signals for the operation modes, respectively, in the form of signals which differ from each other in respect to frequency.
In a yet further preferred mode for carrying out the invention, the mode setting means may be so arranged as to output the control signals for the operation modes, respectively, in the form of signals which differ from each other in respect to voltage level.
In a still further preferred mode for carrying out the invention, the rate-of-change setting means may be so implemented as to set the rate of change of the field current in changing-over of the operation mode from the battery charging operation mode to the high-voltage operation mode smaller than the rate of change of the field current in changing over of the operation mode from the high-voltage operation mode to the battery charging operation mode.
The identifying means may preferably be so arranged as to output the result of discriminative identification of the content of the control signal inputted from the mode setting means upon setting of the battery charging operation mode or upon setting of the high-voltage operation mode and converts the control signal to a voltage of a level corresponding to the operation mode as set, while converting the voltage to a voltage level corresponding to the control signal for the low-voltage operation mode with a predetermined time constant, to thereby set a rate of change of the field current for the low-voltage operation mode in the rate-of-change setting means.
The identifying means may preferably be so arranged as to invalidate a field current interruption control signal outputted in accordance with results of battery terminal voltage detection and rectifier output voltage detection, respectively, upon identification of the low-voltage operation mode.
The voltage regulator may preferably include an output voltage detecting means for detecting an output voltage of the AC generator. When the output voltage lowers below a predetermined value, the rates of change as set in the battery charging operation mode and the high-voltage operation mode is invalidated to thereby allow the field current to increase at a higher rate of change.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.